1. Field of the Invention
The present invention relates to an optical waveguide light emitting apparatus and light emitting method which employ an electroluminescent (EL) emission as a light source and can emit the EL light or EL-oriented light as a linear beam or a laser beam.
2. Description of the Related Art
Conventionally, linear beams have been heavily used, and among the linear beams, a laser beam has been favorably used in various areas since it is a highly directional coherent light with a sharp spectrum width. For example, a diode laser apparatus which employs a solid laser of an inorganic semiconductor such as GaAs, i.e. semiconductor laser, is widely known as an emitting apparatus of the laser beam. In general, the diode laser apparatus uses a light emission induced by a recombination of injected electrons and holes at a laser cavity, and it is mandatory for the use to satisfy the both electric conditions, e.g. potential drop and Ohmic loss, and the optical conditions, e.g. refractive index difference. Regarding the inorganic semiconductor, a relatively thick layer may be used without severely sacrificing the potential drop and Ohmic loss since it shows high carrier mobility, and a planar waveguide laser and a distributed Bragg reflection vertical cavity laser may be easily manufactured since a semiconductor material with a large refractive index difference can be used. Thus, an inorganic semiconductor laser which uses the inorganic semiconductor has been actively developed since it satisfies the both conditions relatively easily.
However, the inorganic semiconductor laser has various problems. For example, the inorganic semiconductor laser is expensive. Also, the apparatus thereof is large in size, and the modulation is not easy. Moreover, since the wavelength of a laser beam is specified by the types of the semiconductor materials, a laser beam having an arbitrary wavelength cannot be obtained, and the applications are limited. The production of a light emitting apparatus which costs less and is smaller in size than a conventional semiconductor laser, provides easy modulation and emits a linear beam having a different wavelength from that of a conventional laser beam has been desired.
Under such circumstances, an apparatus or a method which can emit a linear beam by means of an organic EL element has been proposed (Japanese Patent (JP-B) No. 3675665). The proposed apparatus is comprised of a first region and a second region, where the first region is composed of a flat light emitting element (organic EL element) including a conductor layer (positive electrode) 26, an organic light emitting layer (EL emitting layer) 27 and a conductor (negative electrode) 28 laminated in this order, and the second region is composed of a flat optical waveguide including a cladding layer 31, a core layer 32 and a cladding layer 33 laminated in this order. The apparatus extracts an incoherent EL light generated in the organic light emitting layer (EL emitting layer) 27 from the side of the conductor (negative electrode) 28, and it absorbs this incoherent EL light into the core layer 31. A light emitting material existing in the core layer 31 is excited by the EL light to emit a coherent light, and the apparatus waveguides the coherent light from the light emitting material and emits an output light 33 from the end of the core layer 31.
However, about 80% of the incoherent EL light generated in the organic light emitting layer 27 in the organic EL element leaks from the end of the organic light emitting layer 27, and only 20% of the total incoherent light is radiated to the flat optical waveguide from the layer surface of the organic light emitting layer 27 (N. C. Greenham, et al. Advanced Materials, Vol. 6, p. 491 (1994)), indicating the low utilization efficiency of the EL light 29 and the insufficient luminous intensity. In addition, in order to provide a laser oscillation in a flat medium by means of a light excitation, the density of the excited molecules per unit area in the medium is important instead of the amount of the excited molecules in the medium as a whole. The flat optical waveguide of this apparatus should have an area approximately equal to that of the layer surface in the organic EL emitting layer. Naturally, the excitation density should be approximately equal to that of the organic EL emitting layer. However, the excitation density of a light emitting layer in an organic EL element is in general smaller than the excitation density required for laser oscillation. Therefore, the apparatus has a problem that a laser oscillation cannot be provided.
Furthermore, Japanese Patent Application Laid-Open (JP-A) No. 2002-156536 proposes an organic semiconductor layer which is composed of a positive electrode layer, a hole transport layer, a light emitting layer including an organic pigment material, an electron transport layer and a negative electrode layer. Since the positive electrode layer of this organic semiconductor layer is an ITO layer disposed on a glass substrate, absorption loss occurs in the EL light generated in the light emitting layer. In order to protect this absorption loss and at the same time to extract efficiently the EL light from the light emitting layer, the thickness of the electron transport layer and the electron transport layer should be increased, i.e. the thickness of 0.1 μm at present should be increased to several μm. Also, the electric current density which is injected in the element should be largely increased, i.e. the electric current density of up to 10 A/cm2 at present should be increased to 1,000 A/cm2. For these increases, the charge transport properties of the hole transport layer and the electron transport layer should be significantly improved, but it is difficult to find such hole transport layer materials and electron transport layer materials. Also, the proposal of this organic semiconductor laser does not disclose a light guiding method of the EL light extracted from the light emitting layer. Therefore, the organic semiconductor laser is not guaranteed for the practical performance and thus cannot be used as an apparatus with the performance equal or superior to that of a conventional laser apparatus.
Meanwhile, JP-A Nos. 2002-111101 and 04-242982 propose an optical waveguide laser light source apparatus which contains an optical waveguide core and an optical waveguide cladding. This apparatus uses a semiconductor laser as a light source, and thus it has various problems as mentioned above. That is, the apparatus is expensive and large in size, and the application is limited because the wavelength of a laser beam is specified by the types of the semiconductor materials and a laser beam at an arbitrary wavelength cannot be obtained.
Therefore, a laser apparatus which uses an EL element as a light source has not yet been commercially available, and the production of an optical waveguide light emitting apparatus and light emitting method which use an EL element as a light source, can emit an EL light generated in the organic EL element or an EL-oriented light as a linear beam or a laser beam and can be favorably used in various areas have been desired.
The present invention is aimed at providing a high-performance light emitting apparatus which resolves the conventional problems, can emit an electroluminescent (EL) light or an EL-oriented light as a linear beam or a laser beam, costs less and is smaller in size than the semiconductor laser, can emit a linear beam having a wavelength different from that of a conventional laser beam, enables easy modulation and is favorable in various fields; and a light emitting method thereof.